Effects of inclusion of decorticated cowpea in layer chicken diets on laying performance and egg quality

Semere Teklemichael Haile¹, Joyce Gichiku Maina¹, Samuel Kesete Ghirmay² and Charles K Gachuiri¹

¹ Department of Animal Production, Faculty of Veterinary Medicine, University of Nairobi P O Box 29053-00625, Nairobi, Kenya
semere6teklemichael@gmail.com
² Department of Animal Science, Hamelmalo Agricultural College. P.O. Box 397 Keren, Eritrea

Abstract

In Eritrea, the primary protein source in poultry diets is fishmeal, derived from anchovies. However, this ingredient is both expensive and seasonally limited, leading to elevated production costs. To explore alternatives, a study was conducted to assess the effect of incorporating decorticated cowpea seeds (DCP) into the diets of brown egg-laying Tetra chickens. A total of 200 chickens, 44 weeks old, were divided into five dietary treatments with varying levels of DCP0: 0% (Control), 5% (DCP5), 10% (DCP10), 15% (DCP15) and 20% (DCP20). The trial lasted for 8 weeks, following a 2-week acclimatization period and data were collected on feed intake, egg production and egg quality. Feed intake was influenced by the treatments, with the highest intake recorded in the control group (132.4 g/day/bird) and the lowest in DCP20 (126.8 g/day/bird). As the DCP level increased, feed intake decreased. Hen-day egg production also showed differences, ranging from 83.6% (control) to 78% (DCP20). Importantly, there was no notable difference between the control and DCP10 (10% DCP), indicating that up to 10% DCP can be incorporated into the diet without negatively affecting egg production. Egg weights across treatments were comparable, without notable differences observed, ranging from 59.5 to 61.6 grams. Other egg quality parameters, such as specific gravity, yolk color, eggshell thickness, shell weight and shell-to-egg weight ratio, also were not influenced by the inclusion of decorticated cowpeas in the treatment diets.

Overall, the study concluded that while the inclusion of DCP affected feed intake and hen-day egg production, it did not have a notable impact on egg quality or feed conversion ratio. It was recommended that DCP be safely included in layer diets up to a 10% inclusion level without compromising productivity or egg quality.

Keywords: chickens, dcp, egg production, feed intake, egg quality, egg weight, fishmeal, protein, poultry diets

Introduction

The poultry industry plays a substantial role in global agriculture, contributing to food security by providing essential proteins through eggs and poultry meat, especially as the global population rises (Daghir, 2001). In East Africa, small-scale agriculture dominates, with poultry farming, particularly chicken rearing, serving as a key component. Chickens are easy to manage, require minimal space and offer smallholder farmers a reliable source of protein and income (Pius et al 2021).

Eritrea, with its rich diversity of livestock species adapted to various agroecosystems, ranks among the highest globally in per capita livestock holdings (AU IBAR, 2016). In 2021, Eritrea's poultry population stood at 2.5 million, consisting of 500,000 exotic layers and 2 million indigenous chickens (MoA, 2021). For poultry health and productivity, a well-balanced, nutrient-rich diet is essential to produce high-quality meat and eggs, prevent diseases and enhance overall bird well-being (Adolwa et al 2021).

A major challenge in poultry farming is the high cost and limited availability of quality protein sources, which make feed the most expensive component of production, accounting for 60-70% of total costs in intensive systems (Thirumalaisamy et al 2019). In Eritrea, fishmeal from anchovies is the main protein source in poultry diets (MoA Eritrea, 2021). However, its high cost and seasonal unavailability drive up poultry production costs (Tesfamichael and Pauly, 2016).

Cowpea seeds offer a promising alternative as a protein-rich, affordable legume. Cowpea, originating from Africa and Asia, thrives in tropical regions, including Eritrea (Taiwo, 1998; Kumar, 2011). It is more heat and drought-tolerant than other crops, making it ideal for Eritrea's climate (Ehlers and Hall, 1996). Mature cowpea seeds provide 22-24 grams of protein per 100 grams, along with carbohydrates, fiber, fat and essential minerals like phosphorus, calcium and iron (Asante et al., 2007). However, raw cowpeas contain anti-nutritive factors that reduce their nutritional quality (OECD, 2016), but these can be mitigated through processing techniques like decorticating, germinating and roasting (Famata et al 2013).

This research aims to evaluate the effects of incorporating decorticated cowpea seeds (DCP) at various levels into the diets of Tetra-layer chickens. It will assess the impact on production performance, feed utilization and egg quality, exploring the potential of cowpeas as a sustainable, cost-effective protein source for poultry in Eritrea.

Materials and methods

Research area

The study was carried out in Keren, Eritrea. Keren is the second largest city in Eritrea, situated at a latitude of 15° 46' 40.51" N and a longitude of 38° 27' 3.85" East. It is located at 1390 meters above sea level and 91 km northwest of the capital city, Asmara. Keren has a hot semi-arid climate, with an environmental temperature between 22 and 30⁰C. The area experiences two main seasons, a wet season from June to September and a dry season for the remaining months. The annual rainfall ranges from 400-500mm/year. The experimental procedure was approved by the faculty of Veterinary Medicine Biosafety, Animal Use and Ethics Committee (University of Nairobi) with Ref: FVM BAUEC/2024/543.

Experimental Birds

A total of 200 Tetra brown birds, aged 44 weeks were randomly selected from a flock of over 2000 birds from one large commercial layer farm. The birds were previously vaccinated against Marek’s disease at hatching, Gumboro at two weeks of age, Newcastle disease at 2, 4, 8 and 16 weeks of age and fowl pox at 11 weeks. The debeaking process was done at the first week and 16 weeks of age. The birds were allocated to five dietary treatments. Each treatment was replicated 4 times, with 10 birds per replicate in a completely randomized experimental design. The birds were weighed and assigned to the five dietary treatments with approximately similar weights. The average live body weight of the selected birds in each treatment ranged from 1942g to 1966g.

House Management

The birds were housed in a well-ventilated house with natural lighting for a relatively constant period of about 12 hours per day. The chicken house temperature ranged from 20-28 ºC throughout the experimental period. The house measured 20m by 5m, in which a total of 20 cubicles partitioned with chicken wire mesh on all sides were built. The five groups of birds were assigned to a cubicle measuring 1.6m in length, 1 meter in height and 1 meter in width, with a floor area of 1.6 square meters. The floor system was a deep litter system. One feeder one drinker and two laying troughs measuring 30cm by 30 cm were provided for each replicate. Water was provided ad libitum.

Source of raw materials

All the feed ingredients and other materials used for the experiment were locally sourced. Cowpeas were purchased from one of the cereal traders in Keren.

Experimental diets

The cowpea seeds were dried in sunlight for two days. They were then ground coarsely at a grinding machine, causing the outer cover to detach from the seed. Next, a blowing machine separated the outer cover (which contains most of the antinutritional factors) into a different container. The seed part was ground again and mixed with other ingredients in varying amounts.

Five iso-caloric and iso-nitrogenous diets were formulated, including the control and experimental diets. The control group received a conventional diet comprising fish meals, whereas the experimental groups received diets containing different amounts of decorticated cowpea seeds (5%, 10%, 15% and 20%). All the treatment diets were formulated to be isocaloric (2750 kcal/kg DM) and isonitrogenous (16 % crude protein DM) as per recommendations (NRC 1994). The birds were acclimatized to experimental conditions for two weeks before they were fed on their respective experimental diets. Each treatment group was randomly assigned to one of the five diets. Feed samples were collected for analysis of proximate composition, as well as calcium and phosphorous.

Chemical analysis

The proximate analysis of experimental diets and five ingredients (fishmeal, decorticated cowpea, yellow maize, wheat bran and sesame) was carried out in triplicate at the National Animal and Plant Health Laboratory (NAPHL) in Asmara, Eritrea. All the samples were analyzed for, Dry Matter (DM), Crude Protein (CP), Crude Fiber (CF), Ether Extract (EE) and Ash content following the AOAC (2016) procedure.

Egg Production

Egg collection was done twice daily, at 11:00 a.m. and 4:00 p.m., with whole and broken eggs recorded separately. To assess egg production percentage, the total eggs laid were divided by the total number of birds and multiplied by 100, a process repeated daily for every treatment and replication. The hen-day egg production per replicate for the entire period was calculated using the formula;

Feed intake

1.4 kg of feed per replicate per day was weighed and placed into a tarred plastic bucket and assigned to each replicate (9.8 kg/week). The feed was scooped from the respective container and placed into the feeding trough. At the end of each day, any feed remaining in the trough was collected to their respective bucket (feed remaining container). The weekly collected feed was weighed again and the difference in weight of the feed at the end of the week from the 9.8 kg feed was taken as the feed consumed during that week for each group of 10 birds.

Feed Conversion Ratio

Feed conversion ratio (FCR) in layer chickens refers to the amount of feed required for a bird to produce a unit of eggs. Typically measured as the ratio of feed consumed to egg mass produced. The egg mass of each treatment was computed from the number of eggs per treatment multiplied by the egg weight.

Egg weight

Over eight months, the total number of eggs laid in each replicate was collected and examined for any cracks or breakage. Additionally, every two weeks, two randomly selected eggs from each replicate were individually labeled, weighed and recorded. The weight of each egg was measured using an electronic weighing balance with an accuracy of 0.00g units.

Egg-specific gravity

The saline floatation method was used to determine the specific gravity of each selected egg. Egg-specific gravity indicates freshness, determined by days since laid. The egg-specific gravity was determined using 40 eggs chosen randomly 8 eggs from each treatment and 2 from each replication. The saline solutions were made by dissolving a known weight of salt in six liters of water with a specific gravity varying from 1.00 to 1.10 g/cm3 in 0.005 increments (Butcher And Miles 2017). The density of each solution was obtained using a hydrometer and the specific gravity of the eggs was determined by immersing the eggs in the increasing specific gravity solutions. The eggs were immersed in water first, then in each saline solution starting from the lowest specific gravity to the highest. The specific gravity of the solution in which each egg first floated was recorded. The salt solutions were placed in plastic buckets which were well-labeled according to the saline solution’s specific gravity.

Egg yolk color

Eight eggs were selected randomly from each treatment, two eggs from each replicate and carefully broken onto a flat white plate. The assessment of egg yolk pigmentation was conducted using the Roche Yolk Color Fan, a methodology established by Vuilleumier (1969). This system assigns color scores ranging from 1, indicating the lightest shade of yellow to 15, representing the darkest shade of yellow.

Eggshell thickness

Eight eggs from each treatment (2 per replicate) were randomly selected for eggshell thickness determination. Eggshell thickness was measured at three positions of the egg circumference using a 0.001mm precision micrometer screw gauge. The mean value of the three measurements was taken to represent the thickness. The mean values of each treatment were used to represent the thickness of eggshells that were obtained from each replication.

Eggshell weight

Eight eggs, constituting two per replicate, were randomly selected from each treatment for eggshell weight determination. Subsequently, the eggs were broken and the albumin and yolk were meticulously separated from the eggshell. To ensure thorough cleanliness, the eggshells underwent a washing process aimed at eliminating any residual traces of albumin adhering to their surfaces. Following this, the washed eggshells were left to dry under sunlight for 24 hours. The dried eggshells were then weighed using a precise electronic weighing balance.

Eggshell to egg weight percentage

The eggshell percentage was calculated by dividing the eggshell weight by the egg weight and then multiplying the result by 100 as per the formula below:

Data analysis

The collected data was stored in Excel spreadsheets. Statistical analysis was done by one-way analysis of variance (ANOVA) using the GenStat (version 15) statistical package. Significant treatment means were separated using Turkey’s test and the significance level was set at p≤ 0.05.

Results and discussions

Chemical composition of raw materials and experimental diets

Principal raw materials used in the formulation were decorticated cowpea, maize, fishmeal, wheat bran and sesame cake. Some synthetic amino acids, lysine and methionine were also included in the diet formulation to meet the amino acid requirements of the layers at varying proportions. These main ingredients were analyzed for proximate composition consistent with the AOAC procedures 2018. The nutritional contents of the main five ingredients were within the specifications of the Kenya Bureau of Standards KeBS (2014) and NRC (1994). The proximate composition of the raw materials is shown in the table below.

Table 2 below shows the analyzed nutritional composition of the five mixed diets. The values were within the stipulations of the Kenya Bureau of Standards (KeBS) (2014) and NRC (1994) specifications.

The dry matter content of experimental feeds was satisfactory, with an average moisture content of 7.73%, well below the 12% threshold that could lead to mycotoxin contamination. This indicates that the feed used was safe and stored under optimal conditions. The protein content of the diets, ranging from 15.9% to 16.9%, was within the recommended levels for laying hens, which is essential for optimal egg production, feather development, and muscle growth. The crude fiber content averaged 9.1%. Moderate fiber inclusion is beneficial for gastrointestinal development and can improve overall poultry performance, including stabilizing gut health and reducing ammonia concentration in poultry houses (González Alvarado et al 2010). The ether extract content ranged from 3.5% to 4.14%, aligning with recommended guidelines. Supplemental fat in the diet can enhance feed efficiency and egg production, particularly when dietary fat is well-balanced. Ash content, crucial for calcium provision, ranged from 8.33% to 14.32%. The calcium levels were within the acceptable range, essential for bone development and eggshell formation, though phosphorus contents (0.7%) were slightly higher than the 0.40% to 0.64% reported by Wang et al (2020). Metabolizable energy (ME) in the treatments averaged 2737.80 Kcal/kg, slightly below the recommended 2750 Kcal/kg, but this did not affect hen’s performance. The study also highlighted the economic benefits of incorporating decorticated cowpeas into the diet. This substitution resulted in a cost reduction, with the cost per kilogram decreasing from 17.2 (control) to 16.9 Nakfa per kilogram in DCP20.

Effects of decorticated cowpea diets on production performance and feed utilization

Table 3 below shows the effects of the inclusion of decorticated cowpeas on the layer's daily egg production, feed utilization and daily feed intake with five diets mixed with varying levels of decorticated cowpeas.

In this study, the average hen-day egg production was higher in birds fed the control diet (83.6%) and the DCP0 diet (83.0%) compared to those receiving higher levels of decorticated cowpeas in the DCP15 and DCP20 diets (79.5% and 78.1%, respectively). The inclusion of decorticated cowpeas in the diet affected egg production (p<0.05), with a general decrease observed when the proportion of cowpeas exceeded 10% (Table 8).

This observation was similar to that of Ysmaw et al (2021) who reported that the group fed with 7-8% of Decorticated cowpeas had the highest egg production percentage. However, the total egg production percentage in this experiment was much higher than that reported by Ysmaw et al (2021) of 55.94% and Balaiel (2009) (69.10%) who reported much lower egg production when decorticated cowpeas were fed to layers. Although the egg production percentage observed in this experiment was higher than that Ysmaw et al (2021) and Balaiel (2009) reported. The production was also less than that recommended by TETRA-SL LL, (2019) which stipulates that production at the same age, should be around 90%. According to Klasing et al (2000), appropriate nutrition is necessary to develop a robust immune system, enhancing disease resistance and higher production rates. The birds used in the experiment were purchased at 44 weeks of age and there was uncertainty about the nutritional management during their earlier life. These results are similar to the findings reported by Igbasan and Gunter (1997) who observed a reduction in egg production, by increasing the level of cowpeas in layers diets. Cowpeas are rich in protein, minerals and energy but contain anti-nutritional factors like trypsin inhibitors and polyphenols. Trypsin inhibitors, for instance, can reduce methionine absorption (Oboh et al 1998). Techniques like de-hulling and heat treatment help reduce these factors (Ene-Obong And Obizoba 1996). In this study, cowpeas were decorticated without soaking, possibly leaving anti-nutritional factors intact, contributing to reduced feed intake and egg production. Breed types and age of birds could be contributing factors to the observed lower production compared to the recommendations.

Figure 1. Effects of inclusion of different levels of decorticated cowpea on daily egg production performance

There were no notable differences in egg weight between treatments. The average egg weight of all the treatments was 60.6g. Egg weight is mainly affected by the bird's breed, hen size, age and nutrition (Tůmová 2016). Results from this study show that egg weight was not prominently affected by the amount of decorticated cowpea inclusion (p=0.328). For birds fed diets based on DCP, the highest egg weight was observed in those birds fed on DCP20 receiving diets containing 20% DCP (61.6 g), while the lowest egg weight was observed in those birds fed on DCP5 receiving diets containing 5% DCP (59.5g). Studies by (Tang et al 2017; Aalaei et al 2019) have reported that the mean average weight of eggs for hybrid birds is between 53.6 to 70.9g. According to the recommendation of TETRA-SL LL, (2019), the average egg weight for TETRA SL brown egg-laying hens at the age of 44-52 weeks is 64.6g. The mean egg weight in this study was 60.6g, which is smaller than the standard size for TETRA birds of the same age. In another study by Balaiel (2009), the average egg weight obtained by feeding decorticated cowpea was 50.1g, which is smaller than the result obtained in this study. The differences in egg weight observed between this study and others can be attributed to factors such as variations in bird breed, age, average body weight, management practices and climatic conditions of the study area.

In livestock production, maximizing efficiency is key, with Feed Conversion Ratio (FCR) measuring feed effectiveness in weight gain or product output. For laying hens, a lower FCR means less feed is required to produce eggs (Li et al 2024). The feed conversion ratio (FCR) in layer chickens measures how effectively chickens convert feed into eggs, which directly affects production costs and profitability. A lower FCR indicates better efficiency, with chickens requiring less feed to produce each egg. The FCR in this experiment was not statistically significant (p=0.361) between treatments, suggesting that the inclusion of Decorticated cowpea in layer chickens' diet did not have any influence on the feed conversion ratio of layers. The lowest FCR of 2.58 was observed in the birds fed the control treatment with 0% DCP, while the highest FCR of 2.70 was observed in the birds fed DCP10 with 10% DCP. The average FCR across all treatments in this experiment fell between 2.58 and 2.70, exhibiting superior efficiency compared to Ysmaw et al's (2021) study, which reported an FCR of 3.98. Additionally, this experiment’s results outperformed Balaiel's (2009) findings, where the FCR stood at 3.26, underscoring the notable effectiveness of this experiment's approach. FCR in layers has been reported to vary from 1.60 to 2.45 (Inatomi 2016: Lokapirnasari et al 2019: Yenilmez et al 2021) which doesn’t agree with the mean feed conversion ratio (2.63) observed in this study.

Good feed intake is crucial for layer chickens to achieve optimal egg production, egg quality and overall health, necessary to provide hens with the resources required for egg formation and laying. Feed intake can affect factors such as shell strength, yolk color and albumen consistency. The highest feed intake (132 g/d/hen) was observed where layers received on the Control diet and those receiving DCP0 (132 g/d/hen). The feed intake for the two groups of layers was higher than that of layers fed on the diet containing higher levels of DCP (Treatments 2, 3 and 4). As the level of DCP increased in the diet, there was a corresponding decline in feed intake. Layers fed on diets containing 15% and 20% had low feed intake which significantly decreased (p< 0.05) with an increase in the level of DCP. The feed intake was lowest in DCP20 (126 g/d/hen). The recommended feed intake for TETRA SL brown laying hens, is 120g/hen/day, in the current study, the feed intake in all treatments was between 126 to 132 g/h/d/ which was slightly higher than their recommendation. The inclusion of decorticated cowpeas in the experiment had an impact on the feed intake of layers. This result is similar to the findings reported by the authors Igbasan and Gunter (1997), who observed that increasing the level of cowpeas in layers diet, caused a decline in feed intake and loss in body weight which led to poor egg production. According to a study by (Erensoy et al 2021), feed intake in layer birds is affected by several factors including genotype, temperature, light and stocking density; such factors can be the possible reasons for reducing the feed intake in the current study. Feed Conversion Ratio (FCR) in layer hens can be improved by optimizing nutrition, providing a balanced diet with essential nutrients and using high-quality feed ingredients to enhance digestibility. Proper lighting (14 hours/day), temperature control (20-28°C) and effective flock management (cleaning, disease control, vaccination) are key to improving productivity and FCR.

Effect of decorticated cowpea diets on egg quality performance

In intensive table egg production, it is crucial to focus on the quality of the eggs produced. It is imperative to produce eggs that are safe, healthy, and biologically sound, while also meeting freshness and quality criteria (Pavlovski et al 2002). Egg quality performance in layers is influenced by various factors, among which are bird age, induced molt, nutrition, heat stress, diseases and production management system, as documented by Roberts (2004). However, all these factors were controlled in the present study and the only variation was the levels of DCP in the diet. Table 4 below shows the effect of different levels of decorticated cowpea on egg quality performance, including egg-specific gravity, shell weight, shell thickness, egg yolk color and shell-to-egg weight percentage.

The specific gravity of eggs is a key indicator of their quality and freshness (Silversides et al., 2001). This measurement helps assess the internal composition of an egg, particularly the ratio of its contents to the shell weight (Malfatti et al 2021). By measuring specific gravity, we can assess the internal composition of an egg, particularly the ratio of its contents to the weight of its shell (Malfatti et al 2021). As eggs are stored, their shell thickness decreases, increasing the likelihood of cracking and decreasing their Egg Specific Gravity (Stadelman et al 2002). Generally, ESG values of 1.08 indicate good eggshell quality (England et al 2012). The mean ESG in this study was 1.08 g/cmᶾ. There were no notable differences among the treatments (p=0.299), showing that there was no effect of including different amounts of decorticated cowpea on the egg-specific gravity in this study. To ensure accurate egg-specific gravity measurements, it's important to measure eggs within 24 hours of collection, maintain stable solution temperatures and consistently sample eggs in the morning, as afternoon eggs tend to have thicker shells (Gary et al 2003).

Egg yolk color is primarily determined by the pigments in a hen's diet, with yellow-orange pigments like xanthophylls producing darker yolks, while feeds like yellow corn or alfalfa yield medium-yellow yolks and wheat or barley result in lighter-colored yolks (Rootstock 2024). The yolk color score ranged from 11.4 to 11.8, with the control treatment having a mean score of 11.4, which was not significantly different (p=0.182) from the other four treatments. The control treatment, DCP15 and DCP20 the lowest egg yolk color scores (11.4), while DCP5 and DCP10 showed higher egg yolk color scores 11.8 to 11.6 respectively. The color of the yolk in chicken eggs is primarily influenced by the presence of carotenoids, such as xanthophylls, lutein and zeaxanthin, in the diet (Marounek and Pebriansyah, 2018; Kavtarashvili et al 2019). The yolk color index in layers can range from 0 to 15, Vuilleumier J.P. (1969), with lighter colors indicating a deficiency in carotenoids (which leads to a pale-yellow coloration in the yolk) and darker colors indicating a carotenoid-rich diet (as observed in this study). These results differ from those reported by Malfatti et al (2021), in which the yolk color ranged from 6.48 to 7.32. In another study by Nkiambuo et al (2023), the average yolk color in the control treatment was 13.2 which is higher than the current study. Synthetic pigments like canthaxanthin and apo-ester are commonly used in poultry feed to enhance yolk color, though some studies suggest potential negative health effects (Grashorn and Steinberg 2002). Natural alternatives, such as calendula or marigold flowers, can also deepen yolk color, with variations often linked to feed composition (Balnave and Bird 1996).

A proper eggshell weight is crucial for ensuring the structural integrity of eggs, reducing the risk of breakage during handling, transportation and storage, it acts as a barrier against microbial contamination, thus safeguarding the egg's internal content and food safety, as noted by Roberts (2004). In this study, the average eggshell weight of the control group was 5.60 grams, which was statistically not significant (p=0.563), compared to birds fed on diets containing different levels of decorticated cowpeas. Škrbić et al (2020) reported that the average eggshell weight for Tetra brown egg-laying hens was 8.96g, which is higher than the results of the current study.

Conclusions

• The inclusion of different levels of Decorticated Cowpea in layer diets reduced both hen-day egg production and Daily Feed intake of the layers.
  
  
• The inclusion of different levels of Decorticated Cowpea in layer diets did not affect the feed conversion ratio and Egg weight.
  
  
• The inclusion of different levels of Decorticated Cowpea in layer diets did not affect egg quality parameters.

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